The present invention is directed toward the field of direct broadcast satellites ("DBS") also referred to in this application as direct-to-home ("DTH") satellites. In particular, a multi-beam DBS satellite is disclosed that is capable of providing regional as well as global programming in a flexible and spectrally efficient manner. Regional programming is provided by including on-board satellite circuitry for receiving, filtering, switching, combining and formatting numerous regional uplink channels that are included within beams of programming information transmitted from geographically widespread sources on the earth. By using the satellite disclosed herein, spectrally efficient regional programming can be carried out between multiple programming sources transmitting in multiple uplink beams and multiple receivers located in areas served by multiple downlink beams. The flexibility of the present invention is provided by the satellite's onboard switching processor that can connect any uplink signal to any downlink beam and can re-map the connectivity on-the-fly. The invention's spectral efficiency is provided, in part, by the use of multiple beams that can reuse the same uplink and downlink carrier frequencies, or that can use differing frequencies.
Prior art DTH satellites typically have one uplink beam and one downlink beam. These satellites employ a bent-pipe architecture, i.e., they simply receive, amplify and retransmit the uplink signal back to the ground. Since there is only one uplink signal, these satellites must gather all of the programming information at a central ground site ("the central hub"), where the collected programming is typically formatted into the Direct Video Broadcast ("DVB") standard and transmitted up to the transparent bent-pipe satellite. Such a satellite is typically in a geo-synchronous orbit so that its single downlink beam can cover the entire United States, for example.
The DVB standard multiplexes up to six video channels on to a 27.5 Mb/s bit stream. On-board the prior art DTH satellite, the uplink bandwidth is demultiplexed into the individual bit streams and amplified using an associated traveling wave tube ("TWT"). The amplified bit streams are then multiplexed and beamed back to earth over the single downlink beam.
The prior art DBS satellite systems suffer from several disadvantages. First, all of the programming carried by the system must be collected and formatted on the ground at the central hub. This is undesirable because it requires each of the programming sources to transmit its programming to the central hub by a dedicated connection, typically a leased high-bandwidth telephone line, or perhaps a satellite link, both of which can be very expensive to maintain and operate. Second, the prior art systems provide no efficient method of providing regional (or local) programming. The lack of local programming is considered to be the primary reason for lower than expected market penetration rates of DTH TV broadcasts and systems. Currently, DTH satellite subscribers must purchase an external antenna or basic cable-TV subscription in order to receive local programming. The present invention eliminates the need for these extra elements, providing the first complete programming solution for the DBS market. Third, the prior art satellites did not provide on-board connectivity nor did they provide flexible re-mapping of any type of on-board switching device. Therefore, reconfiguring the system to provide programming from several local sources, or combining local and global sources was difficult and expensive to configure. Because of these problems, the prior art systems only provided a set of static global sources of information and no regional programming.
Regional programming is theoretically feasible in the prior art one-beam system by combining the regional programming with the global programming at the central hub. However, because the satellite has only one downlink beam, it would be tremendously wasteful of available bandwidth to try and provide localized programming via the prior art DBS satellites. In effect, the regional programming would be transmitted as if it were global programming, since the prior art satellite has only a single downlink beam. The spectral inefficiency in such a system is obvious, and is precisely why such prior art satellites and DTH systems do not provide regional programming. Since the audience size for the regional programming is smaller, revenues will be smaller, and therefore the satellite operators would rather use the available bandwidth of the downlink beam for global programming. Further adding to the spectral inefficiency of the one beam to one beam system is the inability to reuse carrier frequencies. Since there is only one beam of information going to and from the satellite, the concept of reusing carrier frequencies is not even an option.
Another prior art DTH satellite system is the "Skyplex" system set forth in Canadian publication No. 2,184,123. Skyplex is designed for a single-beam system and provides limited onboard multiplexing and formatting of up to seven single-channel per carrier ("SCPC") sources sharing the bandwidth of a single uplink beam. This satellite design is able to gather video signals from geographically distributed sources, but only within a single uplink beam, not from multiple uplink beams. The satellite then multiplexes the individual channels into a multiple-channel per carrier ("MCPC") DVB format for downlinking over a single downlink beam to home receivers.
Although solving in part the prior art problems associated with routing all of the programming through a central hub, the Skyplex system is limited to a one-beam system and therefore does not provide a spectrally efficient or flexible means for regional programming. It does not provide a means for receiving and transmitting information in a multi-beam system, nor does it provide for flexible frequency reuse in a multi-beam system. It does not provide a mechanism for variable mapping of signals from any source beam to any destination beam or combination of destinations. It does not provide any type of on-board switching and filtering of channels in a multi-beam system, and it is incapable of on-the-fly re-mapping. These functions are desirable in a regional programming system and are not taught by the Skyplex reference.
Therefore, there remains a need in this art for a multi-beam satellite capable of providing spectrally efficient regional programming in a flexible manner.
There remains a more particular need for such a satellite having the ability to link together different geographic sources of information uplinked directly to the satellite in different uplink beams and to format these sources into a digital standard compatible with DTH satellite systems.
There remains a further need for such a satellite having the ability to map any uplink channel of information to any downlink beam in the multi-beam satellite, and to flexibly re-map the connectivity on-the-fly, without tremendous cost or complexity.
There remains another need in this art for a DTH satellite that is capable of receiving, switching, combining and formatting both global programming and regional programming in a bandwidth efficient manner.
There remains yet another need in this art for such a satellite that is capable of receiving uplink information from the conventional central-hub station, which transmits the global programming to the satellite, as well as receiving uplink information from numerous regional stations distributed throughout the geographic areas served by the satellite.
There remains a further need for such a satellite that can extract or filter the individual channels of uplink information from the global and regional programming, switch this information onto a set of downlink beams, and format the switched downlink information into a digital TDM broadcast standard, such as the DVB format.
There remains an additional need for such a satellite that includes a switching processor and a formatting processor, the switching processor for filtering and switching the incoming uplink channels of information from the regional stations and possibly from a central station, and the formatting processor for combining the switched channels and formatting them into a downlink beam according to a predetermined digital broadcast format.